1. Technical Field of the Invention
The present invention relates to local area network switching apparatuses for routing and bridging data transfers to other networks of a different type. The invention further relates to transferring messages between networks having non-compatible network interfaces and different data link protocols. The disclosed system relates to bridging between networks using special-purpose hardware.
2. Background Art
Presently, numerous types of networks coexist in the telecommunication industry, such as Local Area Networks (LANs), Wide Area Networks (WANs), X.25 Networks, Integrated Services Digital Networks (ISDNs), and Asynchronous Transfer Mode (ATM) Networks. Because of the existence of different networks and standards, there is a need in the telecommunications industry for communication between data processing devices connected to heterogeneous networks. As an example, owners of previously installed LANs frequently want to connect to the emerging broad band Integrated Services Digital Network (ISDN) or ATM Networks.
In a worldwide effort to harmonize the development of networks and the data processing devices associated with them, international organizations like the Comite Consultatif International de Telegraphe et Telephone (CCITT), the European Computer Manufacturers' Association (ECMA), and the International Organization for Standardization (ISO) have established standards for each type of network. ISO has developed a general framework to serve as a reference for all existing and future standards, called the reference model of Open Systems Interconnection (OSI). Most existing and newly developed standards claim to be OSI compatible. This model is a universally applicable logic structure or layered architecture, containing seven layers as shown in FIG. 1. Each layer has a set of defined functions and provides a set of services to and from the adjacent two layers.
LAN switches are widely used by industry to interconnect multiple Ethernet or Token Ring LANs through a switch so that devices on one LAN can communicate with devices on other LANs. New LAN switches are being developed to interconnect networks having various data link (layer 2) protocols to enable various LAN segments to connect to ISDN or ATM networks. This merging technology requires a format conversion between the different protocols used on the networks.
Much prior art has dealt with the format conversion of one network protocol to another. In U.S. Pat. No. 5,341,376, "An ATM Cell Format Conversion System," Yamashita teaches an ATM cell format conversion system. ATM means Asynchronous Transfer Mode, which is the current popular method for transmitting speech, data, and pictures over the Internet. An ATM cell is the basic unit in which data is transmitted. An ATM cell is comprised of 53 octets of data, where an octet is another term for byte or eight bits of data. The 53 octets are subdivided into five octets for carrying header information for the message being transmitted including the message destination and 48 octets for carrying message data. A message is segmented into ATM cells as it is sent to the Internet and then reassembled from ATM cells at the destination.
Yamashita has found that when transmitting messages formatted into 53 ATM octets over telephone lines using older techniques, such as Synchronous Transfer Mode (STM), the standard ATM format is not totally compatible. For STM, Yamashita found that better efficiency can be attained for transmitting ATM cells over STM media by adding an idle (dummy) octet to each ATM cell and thus comprising an ATM cell of 54 octets rather than 53. Yamashita teaches an ATM cell format conversion system to generate 54 octet cells from 53 octets cells. Like Yamashita, the present invention uses ATM transmissions, but Yamashita does not use the standard ATM format. Yamashita converts the basic ATM format of transmission from 53 to 54 octets. This makes Yamashita's ATM non-standard and not used by the rest of the industry. The present invention uses the standard ATM solution having 53 octets, never attempts to modify the standard approach, and does not use Yamashita's invention.
In U.S. Pat. No. 5,323,392, "Adaption Device and Method for Efficient Interconnection of Data Processing Devices and Networks" by Ishii et al., Ishii teaches an adaption device for connecting processing devices and networks which have different protocols. Ishii's adaption device for connecting processing devices and networks which have various layer 2 (link layer) protocols of the HDLC (High Level Data Link Control) type. HDLC is the standard used most commonly for layer 2.
Ishii's adaption device interconnects two different protocols of the HDLC generic type: 1) Link Access Procedure on the D Channel (LAPD), which is Link Access Procedure Balanced (LAPB), which is specific to LANs. An HDLC frame, incoming from a first data processing device complying to the first layer 2 protocol of the LAPB type, is stored within the adaption device. The frame is then mapped to a second layer 2 protocol of the LAPD type and forwarded to a network interface. The layer 2 mapping function resides in a Programmable Read-Only Memory (PROM), a receive frame is stored in adapter memory, and the mapping function between layer 2 protocols is done by a microprocessor.
The present invention, like Ishii, features methods for adapting different layer 2 protocols. The present invention maps switch header to ATM control header but uses hardware rather than a processor to do the mapping function. Ishii's solution is related to slower network transfer rates where slower microprocessor controlled mapping is permissible. The present invention is for higher speed networks where Ischii's processing mapping speeds are not acceptable.
In U.S. Pat. No. 5,581,558, "Apparatus for Bridging Non-Compatible Network Architectures" by Horney et al, Horney teaches a bridging apparatus for sending data to and from a local area network (LAN) from and to a wide area network (WAN). Horney's invention also deals with the OSI model of layered protocols of FIG. 1 and with various layer 2 protocols. Horney chooses a popular wide area network standard called X.25, which is based on the Comite Consultatif International de Telegraphe et Telephone (CCITT) definition of the lower three layers of the OSI model. Horney converts the X.25 protocol to a 1 Mb (StarLAN) local area network, which is an IEEE 802.3 Carrier Sense multiple Access with Collision Detection ((CSMA/CD) LAN protocol. The layer 2 mapping function resides in a Read-Only Memory (ROM), a receive frame is stored in adapter memory, and the mapping function between layer 2 protocols is done by a microprocessor.
Both Horney and the present invention feature methods for bridging data between different layer 2 protocols. However, the present invention maps switch header to ATM control header but uses hardware rather than a processor to do the mapping function. Horney's solution is related to slower network transfer rates (56 Kbits/sec) where slower microprocessor mapping is permissible. The present invention is for higher speed (155 Mbits/sec) networks where processing mapping speeds are not acceptable.
In U.S. Pat. No. 5,577,039, "System and Method of Signal Transmission within a Plesiochronous Digital Hierarchy Unit Using ATM Adaption Layers" by Won et al., Won teaches a format conversion system for converting the plesiochronous digital hierarchy (PDH) data transmission format to the ATM data transmission format and for converting ATM to PHD. PHD is a scheme for multiplexing several 64 Kbit/sec ISDN channels together to produce a higher bit rate signal. Like the other prior art solutions, Won uses memory and a microprocessor in the conversion system to perform the mapping functions between the two protocols being converted. The present invention neither maps PDH to ISDN nor uses microprocessor control in bridging between networks.
In U.S. Pat. No. 5,619,650, "Network Processor for Transforming a Message Transported from an I/O Channel to a Network by Adding a Message Identifier and then Converting the Message" by Bach et al, Bach teaches converting an I/O Channel format to a LAN format. Bach's invention for the most part is not related to the present invention. Both Bach and the present invention feature methods for adapting two dissimilar interfaces; however, the present invention maps switch header to ATM control header but uses hardware rather than a processor to do the mapping function. Bach maps a standard I/O Channel to a LAN using a processor.
In U.S. Pat. No. 5,568,477, "Multipurpose Packet Switching Node for a Data Communication Network" by Galand et al., Galand teaches a multi-purpose packet switching network node capable of switching packets received on any number of node input ports to any number of output ports. The node can receive either ATM cells or variable length messages on any input and switch that input to any switch output of the node. Reformatting is involved of both ATM or variable length (VL) messages to a packet format, which is basically comprised of pseudo ATM packets that carry segmented VL data.
Both Galand and the present invention feature methods for adapting a protocol to the ATM cell format and both apply to switches. However, Galand's solution adapts a variable length message, like that used for a circuit switch, to the ATM cell format using a microprocessor and defines a switch that switches ATM cells. The present invention uses a switch that switches LAN frames and not ATM cells.
The present invention also teaches an increased throughput capability between networks. Prior art includes U.S. Pat. No. 5,457,681, "ATM-Ethernet Portal/Concentrator" by Gaddis et al. Gaddis teaches an Ethernet to ATM converter. Gaddis expands the distance an Ethernet segment (which is a LAN) can transmit a message by connecting the Ethernet segment to an ATM Network. In fact, Gaddis connects multiple Ethernet segments to a multi-ported ATM Network, whereby he enables a first Ethernet segment to send messages to a second Ethernet segment through the ATM Network. Gaddis features a dual-ported memory with the ATM input and output controlled by a DMA controller and the Ethernet input and output controller by an Ethernet controller. A processor is required to control and program both the DMA and Ethernet controllers. Messages from either source are stored in the dual-ported memory depending on which direction the message is traveling. Both Ethernet and ATM headers are generated directly from the memory with the help of the controllers. This method also enables message broadcast to occur from the dual-ported memory, thus eliminating a need to copy the data from an external memory if the message is broadcast.
Gaddis claims the invention to be used as either a portal or a concentrator, where a portal connects one Ethernet segment to one port of an ATM network and a concentrator connects multiple Ethernet segments to one ATM network. For the concentrator, a bus is used to interconnect the multiple Ethernet segments, and the bus goes to one port of the dual-ported memory. The bus becomes a bottleneck for the concentrator, and the performance is questionable and depends upon improving the performance of the bus.
Both Gaddis and the present invention feature methods for connecting LANs to ATM networks and for converting messages in LAN formats to messages in ATM format. The present invention only deals with a switching approach for interconnecting multiple LANs to multiple ATM ports. Multiple connections are supported simultaneously through the LAN port switch. The present invention is neither a single portal approach nor a concentrator. Gaddis's invention functions as a portal or a concentrator and does two basic operations: 1) converts Ethernet messages to ATM messages and 2) converts ATM messages to Ethernet messages. In contrast, the present invention is for a LAN switch or hub which either bridges or routes LAN messages or ATM messages. The present invention also performs LAN emulation and supports virtual LANs. Gaddis uses software control by a processor, and the present invention is more efficient using an all hardware solution.
In U.S. Pat. No. 5,303,344, "Protocol Processing Apparatus for use in Interfacing Network Connected Computer Systems Utilizing Separate Paths for Control Information and Data Transfer" by Yokoyama et al., Yokoyama teaches a communication control equipment connected between a computer and a network to expedite the sending and receiving of messages. The control of the complete message prior to Yokoyama's invention was accomplished by the software of the computer only. A communication control equipment is introduced as new hardware to take the some of the processing burden off of the computer. The computer still does some of the message control, and some is off-loaded to the new hardware. The invention takes mainly a parallel processing approach in that the communication control equipment is comprised of multiple processors, each of which relieve the computer of one of the message control tasks.
There is a similarity between Yokoyama and the present invention in that both use additional hardware to improve the speed of processing messages. Another slight similarity is that Yokoyama splits a single message into two different processing paths internal to his additional hardware. Likewise, the present invention uses two different processing paths. However, Yokoyama uses multiprocessors in his new hardware to improve the performance of messages, where the present invention uses special-purpose hardware to further improve performance. The present invention is better, because general purpose processors cannot handle a specific task as quickly as special hardware can.
Yokoyama splits a single message into two paths sending control information down one path and data down the other. The present invention segregates different types of messages by path, sending bridged messages requiring layer 2 conversions down one path in their entirety and routed messages requiring layer 3 conversions down a second path in their entirety. In addition, Yokoyama deals with the scenario of a plurality of computers connected to a network. Communication between computers uses a single homogeneous message protocol, where all messages are comprised of the exact same protocol and format. The protocol includes a complex control structure, wherein first a sequence of messages is used to establish a connection through the network by the computer requesting a specific connection, the network establishing the connection path and sending an acknowledge message back to the computer. Next, the computer sends data over the established connection, wherein a single or multiple messages can be transferred. When the computer is finished using the connection, it then sends a message to break the connection. In contrast, the present invention deals with a switch hub scenario which receives heterogeneous messages of various protocols from local area networks (LANs) and Asynchronous Transfer Mode (ATM) messages. The heterogeneous messages are either routed by the switch hub or bridged from one hub input port to another hub output port. The present invention therefore deals with multiple different message protocols and converts a first message protocol to a second message protocol using special purpose hardware (no processor) to expedite the conversion.
Other prior art which is not as closely related is disclosed in the article, "High-Speed Serial Interface MicroChannel Adapter", in the IBM Technical Disclosure Bulletin, Vol. 34, No.7A, December 1991. The article discloses a High-Speed Serial Interface (HSSI) for transferring data at 52 Mbit/sec using a pseudo standard which was jointly developed by T3plus Networking and Cisco Systems. The disclosure is of an apparatus for connecting the MicroChannel bus to the HSSI interface. Both the IBM Technical Disclosure Bulletin (TDB) and the present invention feature methods for adapting two dissimilar interfaces. However, the IBM TDB deals with connecting a computer bus to a serial interface, not with interconnecting multiple networks through a switch.
It is the object of this invention to sort incoming LAN messages at each ATM port of the switch into two different paths for efficient routing or bridging between dissimilar networks.
It is a further object of this invention to provide a high performance bridging path between dissimilar networks by implementing the bridging path as a hardware forwarding engine for transmitting LAN frames between LAN ports and ATM ports of the LAN switch.
It is a further object of this invention to provide LAN emulation over ATM networks which permits LAN frames to be transmitted between two different LAN segments interconnected by an ATM network.
It is a further object of this invention to convert formats between different layer 2 protocols using special purpose hardware without the aid of a microprocessor.
It is a further object of this invention to provide two different types of memory queues, one being a software queue of frames to be processed by a microprocessor and the other being a hardware queue of frames to be processed by a hardware forwarding engine.